1. Field of the Invention
The present invention relates to transmissions for vehicles, and more particularly to a method of controlling a transmission of a vehicle in two different modes according to requirements for the quality of control from the view point of power performance and economical performance of the vehicle.
2. Discussion of Prior Art
A transmission for a vehicle generally comprises a gear mechanism and selective engaging means such as friction clutches or one way clutches which selectivity rotationally connect two mutually rotational members in said gear mechanism and friction brakes or one way brakes which selectively brake a rotational member in said gear mechanism relative to a casing structure thereof, and provides selected one of a plurality of speed stages according to the engagement and disengagement of those engaging means. In an automatic transmission in which the engagement and disengagement of the engaging means are automatically controlled by a control means according to operational conditions of the vehicle, in acceleration of the vehicle from stoppage the transmission first provides 1st speed stage and is gradually successively shifted up to higher speed stages such as 2nd, 3rd, 4th and 5th speed stages generally according to the balance between vehicle road speed and throttle opening. It is already well known to apply a restriction to the automatic shifting of the transmission according to the balance between vehicle road speed and throttle opening in order to temporarily modify the performance of the automatic transmission so as to increase the power quality of the vehicle or to ensure better engine braking, by restricting upshifting to the 4th or the 5th speed stage, by shifting a speed shift lever shiftable by hand among D, S and L shift positions. However, in the conventional automatic transmissions for vehicles, regardless of such temporary restrictions to the shifting up of the gear transmission to the 4th speed stage or the 4th and 5th speed stages, the upshifting and the downshifting of the transmission are always performed through all intermediate speed stage or stages. However, when the vehicle is operated in a relatively moderate manner with no great demand for power quality under such a condition that not much load is carried by the vehicle, no great acceleration is required, the vehicle is operated in a region of no high altitude, the engine is operating with all of its cylinders, the engine is sufficiently warmed up, battery is in good charged condition, or the vehicle which incorporates a two wheel/four wheel drive changing over system is operated in two wheel drive mode, it would be possible to operate the vehicle in sufficiently good condition by shifting the transmission up to a higher speed stage directly from the start speed stage or a lower speed stage without passing through an intermediate speed stage so that the vehicle is more often operated at a higher speed stage with a smaller reduction gear ratio and therefore at a lower rotational speed of the engine thereby saving consumption of fuel.